Whipstocks are well known in the oil well drilling art and have been utilized for many decades. A whipstock is an elongated tool having a long, tapered concave interior surface and a long straight cylindrical outside surface. Whipstocks are used in cased borehole and open borehole. This invention relates to cased borehole. The whipstock is set downhole in an oil well such that the concave interior surface thereof provides a guide to a milling tool to mill out an opening in the oil well casing to provide a new, angled direction for additional drilling. While whipstocks have been known for many years, their present use is increasing due to the cost of drilling, making it desirable to drill as many wells as possible off of a central, cased borehole.
In order to utilize a whipstock, it is necessary to set or anchor the whipstock against the casing in the borehole at the location where it is desired to mill a hole through the casing to begin drilling in a new direction. Due to the long, tapered upper end of the whipstock being substantially smooth, it is difficult to design a suitable tool that is attachable to a running string for retrieving the whipstock after it has served its purpose.